1. Field of the Invention
This invention relates to highway delineation, with particular reference to delineation for median barriers which seperate opposing sides of a divided highway.
2. Prior Art
The use of a median barrier between opposing directions of a divided highway provides numerous advantages of safety and traffic regulation. A common form of median barrier is indicated in FIG. 1 and is known to those skilled in the art as a New Jersey-type barricade or barrier. Although plainly visible during daylight hours, the barricade becomes deceptively ill-defined during nighttime driving, particularly where visibility is further hampered by poor weather conditions. It is not uncommon, therefore, to observe tire impact lines along the barrier sidewall, witnessing to a previous lack of perception or misjudgment by a vehicle driver.
To assist driver recognition of such median barriers during poor visibility, techniques of highway delineation have been applied to the barrier structure. The most common method of barrier identification has been to apply reflective buttons 10 (FIG. 1) at the sidewall surface of the barrier such that vehicle headlights are reflected to warn the driver of the barrier location. Such reflective buttons are usually several inches in height and may include a prismatic reflecting means to distribute light through multiple angles of observation, or retro reflective materials to return the light to its original source. Numerous difficulties remain with the use of such reflective buttons and similar barrier delineation techniques, resulting in continued injuries to life and property, in addition to maintenance costs associated with repair and reconstruction of impacted median barriers.
The types of safety problems arising from the use of such delineation techniques include inadequate identification as to the nature of what object is being delineated. For example, when such a reflective button is viewed at a distance during the night it is difficult for a driver to ascertain whether such a reflective button is located on a bicycle, roadside post or median barrier. Obviously, driver reaction will be different with respect to each form of obstacle encountered. This confusion is enhanced when headlights from an oncoming vehicle traveling on the opposite side of the median barrier give a deceptive appearance as a reflector as opposed to a headlight. Such deception is particularly accute where the top or cap of the median barrier is also delineated with reflective buttons, since such barriers are purposely constructed so that headlights from the opposing traffic can be viewed just over the barrier top.
In addition to difficulty in resolution, depth perception of the delineated object is not provided from the reflector type buttons affixed on sidewalls of the median barrier. Such depth perception is invaluable to a driver who is about to negotiate a curve in the road, where rate of curvature is not clearly indicated by mere reflection from an almost point reflective source. Lack of ability to adjust speed because of absence of depth perception is frequently the cause for direct impact at the median barrier wall.
Other problems encountered with current delineation methods include effects of weather in concealing the small reflective buttons at the barrier sidewall. The small reflective surface is quickly concealed by splashed mud, debris, etc. which voids any reflective ability. Furthermore, impact at the reflector by overhanging structure of a truck or vehicle will typically destroy these reflective buttons, resulting in loss of delineation and increased risk to drivers, as well as additional cost for replacement and maintenance. This partial description of safety hazards associated with current delineation techniques suggests the need for a novel approach to median barrier delineation.